“Those who wish to discriminate and say, we believe in some and disbelieve in others, and wish to adopt a way in between -Those are the disbelievers, truly. And We have prepared for the disbelievers a humiliating punishment” (Q, 4:150-152)

Quran is the only source of law.6:114-6:115 proves this.”Say,should I take other then Allah as a source of law when He has revealed the book fully detailed”?
If belief in Hadith was obligatory it would have been mentioned as part of greatest testimony stated in 6:19.

There is a widespread misconception/disinformation about the Ahadith: in the minds of not only the Non-Muslims but also some Muslims, as if they are purely the personal utterances of the Prophet (PBUH); devoid of Divine sanction, hence not to be taken seriously as the Holy Qura’an. Ahadith and Sunnah constitute; the second most important source of Islamic teachings, explanation and practical manifestation, and an integral part of the Islamic Belief. [By denying/ignoring Ahadith and Sunnah one cannot claim to be following the Prophet, as ordained in the Holy Qura’an repeatedly. (Obey Allah and Obey the Prophet) (Q, 4:59) https://shakir2.wordpress.com/2017/12/13/are-ahadith-word-of-god/